Source code for cr.vision.concurrent.on_screen_display

'''
Displays images on screen
'''
import logging
import queue
import threading
import numpy as np
import cv2
from cr import vision as iv
from .base import ActiveNode


class OnScreenDisplay(ActiveNode):
    '''OnScreenDisplay'''

    def __init__(self, input_queue, name='Screen'):
        super().__init__(name)
        self.input_queue = input_queue
        self.finish_event = threading.Event()

    def _operation(self):
        if self.finish_event.is_set():
            # nothing to do
            return
        # check if user has asked for the display to be stopped.
        if iv.wait_for_esc_key():
            # We indicate that display should be stopped now
            self.finish_event.set()
        try:
            # read next set of frames
            token = self.input_queue.get(timeout=1)
            if isinstance(token, np.ndarray):
                # a single frame is to be shown
                cv2.imshow('Output', token)
        except queue.Empty:
            # there were no frames in the input queue
            logging.debug('on screen display: input queue is empty')
            pass

    def _end(self):
        super()._end()
        cv2.destroyAllWindows()